Layered composite material for plain bearings, production and use thereof

ABSTRACT

The invention is a method for the production of a composite multilayer material having a backing layer, a bearing metal layer of a copper alloy or an aluminum alloy, a nickel intermediate layer and an overlay consisting of about 0-20 wt. % copper and about 0-20 wt. % silver, the combined maximum wt. % of copper and silver being about 20 wt. %, the rest being bismuth, and the layer thickness of the nickel layer amounts to more than 4 μm by electrodeposition, in which the overlay is deposited from methyl sulphonic acid-based electrolyte.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a composite multilayer material, in particularfor plain bearings or bushings, having a backing layer, a bearing metallayer of a copper alloy or an aluminum alloy, a nickel intermediatelayer and an overlay. The invention additionally relates to a method forthe production of the composite multilayer material, the production ofplain bearings or bushings and uses for the composite multilayermaterial.

2. Related Art

Conventional composite multilayer materials with the structurecomprising steel backing as backing layer, lead-bronze as bearing metallayer and overlay of lead-tin-copper, as described for example inGlyco-Ingenieurberichte 1/91 (Glyco Engineering Reports 1/91), haveproven themselves as a result of their high reliability and mechanicalload carrying capacity. In such a structure, the overlay iselectrodeposited. Such an overlay is a multifunctional layer, in whichforeign particles may be embedded, which serves as corrosion protection,which exhibits emergency running characteristics and which isparticularly suitable for running-in or conforming of the slidingpartners.

The bearing metal layer also exhibits adequate emergency runningcharacteristics, in case the overlay is completely worn away, at leastin places.

Conventional composite multilayer materials comprise a lead-basedoverlay, a common alloy being for example PbSn10Cu2. Such overlaysexhibit low hardnesses of around 12-15 HV (Vickers Hardness), for whichreason they have good embedding properties and are insensitive toseizure. For reasons of industrial safety and environmental protection,it is nonetheless desirable to replace the lead, which is a heavy metal,with other suitable materials.

One approach is to use hard layers as overlays in heavily loaded bearingsystems. For example, aluminum-tin layers with hardnesses of around 80HV are deposited using PVD (physical vapor deposition) methods. Theseare lead-free, but are very expensive to produce. Such bearings arehighly wear-resistant, but they exhibit almost no embeddability and aretherefore generally combined with soft, lead-containing layers as acounter-shell. However, it is also desirable to replace the lead incounter-shells with other materials.

Attempts have been made to use pure tin as a sliding surface. With ahardness of roughly 10 HV, however, pure tin is even softer than theconventional lead alloys and is therefore incapable of absorbing theloads which arise for example in crankshaft main bearings and connectingrod bearings.

DE 197 28 777 A1 describes a composite multilayer material for slidingelements, the overlay of which consists of a lead-free alloy containingtin and copper, wherein the copper content amounts to 3-20 wt. % and thetin content to 70-97 wt. %. This overlay is electrodeposited by means ofa methylsulfonic acid electrolyte with grain refining additives. Theoverlay produced in this way has the characteristics of ternarylead-based overlays. In order further to improve wear resistance, DE 19728 777 A1 additionally proposes providing hard material particlesdispersed in the electrolyte bath, these being incorporated into thelayer. However, this is associated with additional effort and cost.Between the bearing metal and the overlay it is possible to provide a1-3 μm thick nickel layer together with a 2-10 μm thick nickel-tin layeras diffusion barrier layer.

DE 197 54 221 A1 discloses a composite multilayer material with anoverlay comprising 3-30 wt. % copper, 60-97 wt. % tin and 0.5-10 wt. %cobalt. In this way, the mechanical load carrying capacity is furtherincreased and embrittlement of the bonding layer between overlay andnickel diffusion barrier layer is prevented. The cobalt reduces thetendency of the tin to diffuse towards the nickel. The addition ofcobalt to the alloy, however, makes the electrodeposition process morecomplex, which reduces process reliability. Furthermore, as in DE 197 28777 A1 the 1-3 μm thick nickel layer may be combined with a 2-10 μmthick nickel-tin layer as diffusion barrier.

EP 1 113 180 A2 describes a composite multilayer material for plainbearings, whose overlay has a tin matrix into which tin-copper particlesare incorporated, said particles consisting of 39-55 wt. % copper withthe rest being tin. A characteristic feature of the composite multilayermaterial is, in addition, that not only is an intermediate layer ofnickel of a thickness of 1-4 μm provided, but also a second 2-7 μm thickintermediate layer of tin and nickel is arranged between the nickelintermediate layer and the overlay. By means of the intermediate layersof nickel and tin-nickel, a system is produced which adapts itself tothe load applied, load carrying capacity being increased, according tothermal conditions, by growth of the tin-nickel layer. This compositemultilayer material may be used to produce products for higher loads inmodern, highly supercharged diesel engines. However, the additionallayer is associated with greater processing complexity during productionof the composite multilayer material and thus higher costs.

A plain bearing is known from DE 100 32 624 A1 which comprises a bearingmetal and an overlay of bismuth or bismuth alloy, which is intended toexhibit improved compatibility and fatigue strength. A crucial factor isa particular preferential orientation of the bismuth crystals, which isintended to have reduced brittleness and improved conformabilityrelative to a random orientation of the crystals and relative to singlecrystals. Possible alloys to which reference may be made are alloys ofbismuth with soft materials such as tin, indium, antimony and the like.However, these exhibit the risk that, where these materials are notdistributed uniformly in the matrix, i.e. in the event of variations inconcentration, low melting eutectics are formed. Therefore, thequantities added should be limited to 5 wt. %. In practice, however, ithas become clear that eutectic formation occurs even below the 5 wt. %limit.

The object of the present invention is to overcome the disadvantages ofthe prior art.

SUMMARY OF THE INVENTION

It has emerged that the presence of further phases of copper and/orsilver in the bismuth matrix increases wear resistance. Although theoverlay does not contain any lead, its specific load carrying capacityand wear characteristics are comparable with or better than those ofconventional lead-based layers. The overlay of the composite multilayermaterial according to the invention is conformable and exhibits a highdegree of embeddability with regard to dirt particles. It isparticularly advantageous that no low melting eutectics form in theoverlay.

More precise investigations have additionally shown that bearings ofthis composite multilayer material stabilize themselves on the initiallystill relatively soft overlay in operation after running-in due toheating and form a higher strength surface. This takes place as a resultof the formation of a layer containing bismuth and nickel throughdiffusion of the nickel into the overlay consisting substantially ofbismuth. The resultant overlay is wear-resistant and has a high loadcarrying capacity. By starting with a nickel layer which is at leastapproximately 4 μm thick, it is ensured that the nickel layer is notwholly converted even after the running-in phase.

The metals copper and silver may be present separately or in combinationin the bismuth matrix. Their total content should amount to betweenapproximately 0.5 and 20 wt.%. Advantageously, the total content ofcopper and/or silver should amount to between approximately 2 and 8 wt.%.

Advantageously, the total content of copper and/or silver should amountto between approx. 2 and 8 wt. %.

The overlay should advantageously exhibit a layer thickness ofapproximately 5-25 μm. Layer thicknesses of approximately 4-6 μm areparticularly preferred for the nickel intermediate layer as are layerthicknesses of approximately 6-14 μm for the bismuth overlay. With layerthicknesses of these orders of magnitude, it is ensured that neither thenickel layer nor the bismuth-based overlay is completely converted as aresult of diffusion. This would lead to problems of adhesion orundesired interactions between the bismuth contained in the overlay andthe bearing metal, for example in the case of lead- and tin-containingbearing metal it would lead to the formation of eutectics with very lowmelting points.

Advantageously, the bearing metals are copper-aluminum, copper-tin,copper-tin-lead, copper-zinc, copper-zinc-silicon, copper-zinc-aluminum,copper-aluminum-iron or copper-zinc alloys. Copper- or aluminum-basedbearing metals are preferred, i.e. bearing metals whose copper oraluminum content is between 50 and 95 wt. %.

According to the invention, the composite multilayer material isproduced in that the overlay is deposited from a methanesulfonic acidelectrolyte onto a composite of backing, bearing metal and nickelintermediate layers, wherein the electrolyte contains a non-ionicwetting agent and a grain refining agent containing a carboxylic acid.Resorcinol is present in the electrolyte as an antioxidant. If theoverlay is also to contain silver, thiourea has to be added ascomplexing agent. Thiourea shifts the deposition potential to the effectthat silver and bismuth may be deposited together.

The grain refining agent used is preferably an agent based on an acrylicacid derivative and alkylaryl polyglycol ether. Such a grain refiningagent is sold by Enthone OMI under the name additive L, Cerolyt BMM/T.

The nonionic wetting agent is significant above all in the case ofcopper-containing overlays. It is intended to prevent uncontrolledcopper deposition, in particular on the bearing backing. Nonionicwetting agents based on aryl polyglycol ether and/or alkylarylpolyglycol ether have proven particularly useful. Such nonionic wettingagents are sold by Enthone OMI under the name additive N, Cerolyt BMM-T.

The plain bearings or bushings according to the invention exhibit thegreat advantage that an interdiffusion layer of bismuth and nickel formson running-in under operating conditions, said layer increasing wearresistance. It is possible to encourage the interdiffusion layer toarise by artificial aging of the plain bearings or bushings. For thispurpose, heat treatment at approx. 150°-170° C. has proven particularlyuseful, said heat treatment proceeding for two or more hours to a fewdays.

The composite multilayer material according to the invention isparticularly suitable for the production of crankshaft main bearings andof connecting rod bearings, in particular for the large connecting rodeye.

DRAWINGS

The invention is explained in greater detail with reference to anExample and FIGS, in which:

FIG. 1 shows a section through the bearing metal layer, nickelintermediate layer and overlay of a composite multilayer materialaccording to the invention;

FIG. 2 shows a section through a bearing consisting of the compositemultilayer material according to the invention after the running-inphase; and

FIG. 3 shows the element distribution determined for the bearingaccording to FIG. 2 in the area III-III by energy-dispersive X-rayanalysis.

DETAILED DESCRIPTION

After appropriate pretreatment, a nickel diffusion barrier layer isapplied from a Watt's nickel electrolyte onto a prefabricated bearing ofa composite of steel and a bearing metal of CuPb22Sn.

The bismuth-based overlay is electrodeposited onto the nickelintermediate layer produced in this way. The following aqueous-basedelectrolyte system is used for this purpose:

Bi³⁺ as bismuth methanesulfonate 30-40 g/l Cu²⁺ as coppermethanesulfonate 1-5 g/l Ag⁺ as silver methanesulfonate 0.1-2 g/lmethanesulfonic acid 150-200 g/l additive “N” (Cerolyt BMM-T) 50-70 g/ladditive “L” (Cerolyt BMM-T) 10-20 g/l resorcinol 2-3 g/l thiourea30-150 g/l

If silver methanesulfonate is omitted, so should thiourea be omitted.

Bismuth is used as anode material. The bath temperature for depositionof the overlay is 15-40° C. The current density used is 1.5-4×10⁻² A/m².The distance between the anode and the cathode amounts to 350 mm atmost. The anode to cathode surface area ratio should be substantially1:1 (+/−10%).

FIG. 1 is a sectional image of the layer structure of the compositemultilayer material as described above, with silver methanesulfonate andthiourea being omitted. 1 designates the overlay of copper-bismuth of athickness of 10.3 μm, 2 being the nickel-intermediate layer of athickness of 4.2 μm and 3 being the bearing metal comprising CuPb22Sn.

The boundary line between the two layers 2 and 3 is shown with a whiteline for the sake of greater clarity.

FIG. 2 is a sectional image of a bearing of the composite multilayermaterial shown in FIG. 1 after the operating state has been established,i.e. after the running-in phase. To this end, the bearing washeat-treated for 500 hours at 150° C. The bismuth-nickel layer of athickness of 8.5 μm designated 4 has arisen by diffusion, said layerresulting in a more wear-resistant sliding surface with a greater loadcarrying capacity. That said layer is a bismuth-nickel layer isconfirmed by the energy-dispersive X-ray analysis results illustrated inFIG. 3. The distances on the X axis match the corresponding layerthicknesses in the area III-III of FIG. 2. The overlay 1′ and the nickellayer 2 now have slightly smaller thicknesses of 3.6 μm and 2.4 μmrespectively.

Underwood tests were carried out to assess the performance of bearingsmade from the composite multilayer material according to the invention.In these tests, a shaft with eccentric weights rotates in rigidlymounted connecting rods. The bearing system in the connecting rods takesthe form of the test bearings. The test bearings have a wall thicknessof 1.4 mm and a diameter of 50 mm. The specific load is adjusted overthe bearing width. The speed of rotation amounts to 4000 rpm. Overlayfatigue and wear were measured after 250 hours of continuous operation.The results obtained in this test are listed in Table 1 (Example Nos.5-8). For the purpose of comparison, the values are also indicated whichare achieved with materials according to the prior art (Examples 1-4).

As is clear from the results listed in Table 1, the bearings made fromcomposite multilayer material according to the invention are markedlysuperior to the conventional bearings with a lead-based overlay withregard to overlay fatigue, wear and maximum load to total wear. Bearingswith a nickel intermediate layer of the thickness according to theinvention exhibit, for the same top layer, a markedly higher loadcarrying limit capacity relative to bearings with a thinner nickelintermediate layer (c.f. Examples 4, 5). The additional use of silverand copper additives improves wear resistance significantly relative topure bismuth overlays (Examples 5-8).

TABLE 1 Prior art According to the invention Ex. No. 1 2 3 4 5 6 7 8Composition PbSn5Cu2 PbSn10Cu5 PbSn14Cu8 Bi Bi BiCu3 BiAg5 BiCu2Ag2Thickness of Ni layer in μm 1 2 1.5 1.5 5 4.5 6 5 Max. last in MPawithout 52.5 60 65 50 75 77.5 80 80 overlay fatigue Wear in μm at 60 MPa15 11 9 8 3 2 2 3 Max. load in MPa to total wear 60 67.5 80 75 82.5 92.595 95 of overlay

1. A method for the production of a composite multilayer material havinga backing layer, a bearing metal layer of a copper alloy or an aluminumalloy, a nickel intermediate layer and an overlay consisting of about0-20wt. % copper and about 0-20wt. % silver, the combined maximum wt. %of copper and silver being about 20wt. %, the rest being bismuth, andthe layer thickness of the nickel layer amounts to more than 4 μm byelectrodeposition, in which the overlay is deposited from anaqueous-based electrolyte system comprising: 20-100 g/l bismuthmethanesulfonate, 0.1-30 g/l copper methanesulfonate, 0.1-2 g/l silvermethanesulfonate, 80-250 g/l methanesulfonic acid, 20-100 g/l nonionicwetting agent, 5-40 g/l grain refining agent, 1-4 g/l resorcinol, and30-150 g/l thiourea.


2. The method as claimed in claim 1, wherein the grain refining agent isbased on an acrylic acid derivative and alkylaryl polyglycol ether. 3.The method as claimed in claim 1, wherein the nonionic wetting agent isbased on aryl polyglycol ether and/or alkylaryl polyglycol ether.
 4. Themethod as claimed in claim 1 further including forming the compositemultilayer material into plain bearings or bushings.
 5. The method ofclaim 4 further including heat treating the plain bearings or bushingsfor two or more hours.
 6. The method of claim 5 further includingmaintaining the temperature during heat treatment between 150-170° C. 7.The method of claim 4 further including forming the bearings ascrankshaft main bearings.
 8. The method of claim 4 further includingforming the bearings as connecting rod bearings.